The present invention relates to gypsum board used in the construction of walls and ceilings, and specifically to a lightweight gypsum board suitable for use as wallboard or ceiling board, and which has a comparable cost to conventional 1/2 inch gypsum wallboard.
Gypsum wallboard is well known for use in interior wall and ceiling construction, and its main advantages include low cost, fire retardance and easy workability in construction applications. However, a major drawback of conventional gypsum wallboard is its weight. Conventional 1/2 inch thick wallboard has a weight of between 1650 to 1800 pounds per 1,000 square feet, or pounds MSF, as this value is referred to in the industry. The relatively heavy weight of conventional wallboard sheets makes them cumbersome and fatiguing for installers to work with. This is especially true when wallboard is used for ceilings, since the individual sheets must be supported over the installer's head either by hand or with mechanical supports against the ceiling joists until appropriate fasteners may be employed to secure the board in place.
Prior attempts to lighten wallboard have involved the use of foam or soap slurries to trap air in the gypsum mixture, thus creating a less dense board core. However, the boards resulting from such attempts sometimes lacked the necessary strength for use in wall and ceiling applications. An industry measure of such strength is the pounds of nail pull, or the amount of force required for the board to be pulled over the head of a nail. A preferable nail pull value for wallboard is in the approximate range of between 65 and 85 pounds of force. Other disadvantages of the use of foam as a filler include the fact that the foaming agents generally interfere with proper hydration, crystal growth and setting of the gypsum and may interfere with the cohesive bond between the core and the paper.
Alternative solutions for producing lightweight gypsum board have employed the use of expanded monocellular volcanic ash. When heated, this material expands, forming hollow, relatively watertight spheres. When the spheres are mixed with the gypsum, air pockets are created which reduce board density. Boards have been made from combinations of ash and gypsum which are lighter in weight than conventional wallboard, however such boards lack the requisite strength of conventional wallboard.
Thus, it is a first object of the present invention to provide an improved gypsum wallboard product which is lighter in weight than conventional wallboard, yet has comparable nail pull values.
It is another object of the present invention to provide an improved gypsum building board which may be used for suspended ceilings as well as wallboard applications.
It is still another object of the present invention to provide an improved process for making lightweight gypsum building board and wallboard.